1. Field of the Invention
The present invention relates to a numerically controlled grinding machine and, more particularly, to a numerically controlled grinding machine having an angular type grinding wheel and a control device for controlling the feed of the grinding wheel based upon a control signal from a measuring device which measures the diameter of the cylindrical side of a workpiece.
2. Description of the Prior Art
In the case of grinding the cylindrical side and the shoulder of a workpiece simultaneously, an angular type grinding wheel is moved relative to the workpiece along an inclined path.
Moreover, where the size tolerance to the cylindrical side of the workpiece is narrow, the feed of the grinding wheel is controlled based upon a control signal from a measuring device which measures the diameter of the cylindrical side. However, a problem occurs where the width of the shoulder to be ground is wider than that of a shoulder grinding surface of the grinding wheel.
Namely, when the inner portion of the shoulder and the cylindrical side are ground, the feeding of the grinding wheel is stopped in response to the control signal from the measuring device. However, when the radially outer portion of the shoulder is ground, the feeding of the grinding wheel is stopped based upon NC data which represents the target position of the grinding wheel to grind the outer portion of the shoulder to a designed size.
If the cylindrical side grinding does not finish at a designed diameter, the ground surface of the inner portion Gbb of the shoulder Gb is offset from the designed position along a axis of the work spindle, as shown in FIG. 6. However, since the grinding of the outer portion of the shoulder is controlled based upon not the control signal from the measuring device but the NC data, the ground surface of the outer portion Gcc of the shoulder Gb exists at the designed position along the axis. Therefore, a step S is produced between the outer portion Gcc and the inner portion Gbb of the shoulder Gb, as shown in FIG. 6.